Space History Photo: Joe Walker Beside an X-15 Airplane

In this historical photo from the U.S. space agency, NASA test pilot Joe Walker stands beside an X-15 airplane, following 169,000-foot altitude flight on March 30, 1961. The X-15 flew 199 times from 1959 to 1968 and was an extremely successful aeronautics research program that laid the hypersonics basis for later spacecraft such as the Space Shuttle.

Each weekday, SPACE.com looks back at the history of spaceflight through photos (archive).